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BerkeleyGW-1.2.0

Submitted by jornada on Wed, 08/31/2016 - 18:10

We are excited to announce the release of BerkeleyGW version 1.2.0! This major version is the result of years of work, and includes many new features, performance increase across the board, and several optimizations. Highlights of this new version are summarized below. The new version can be obtained from the downloads page.

Berkeley 1.2.0 (Aug/2016)

Features marked with [*] change the default behavior of the code relative to
BGW-1.1 and may cause a small change in the numbers produced by the code.

New features

1) Added new methods to deal with the frequency-dependence of the polarizability:
1.1) Added Godby-Needs (GN) plasmon-pole model.
1.2) Added spectral method for real-axis (RA) full-frequency (FF) calculations.
The spectral method allows one to compute the dielectric matrix much faster for
many frequency points on the real axis. The old method for RA-FF calculations
is now refered to as the Adler-Wiser method. Still, RA is no longer the default
FF method (see next item).
1.3) Added Contour-deformation (CD) full-frequency (FF) formalism.
The CD is the recommended (and default) scheme for calculations performing an
explicit evaluation of the dynamical effects of the dielectric matrix without
plasmon-pole models. It requires the evaluation of the dielectric matrix on
both real and imaginary frequencies, but with typically a much smaller number
of frequencies. The previous formalism is now refered to as real-axis (RA)
full-frequency (FF) formalism. CD is now the default method for FF calculations.

2) Released non-linear optics post-processing utility.
This codes allows one to compute the inter-exciton transitions in non-linear-optics
experiments.

3) Improved usability in the code output and added dynamic verbosity switch.
BerkeleyGW has now a much simpler and neater output. The code gives time estimates
for most tasks it performs -- at least for those that are more time-consuming.
There is also a run-time flag supported by all codes to switch the amount of
verbosity the code produces. The old compilation flag "-DVERBOSE" is now
deprecated.

4) Improved usability in the code input.
Several input parameters, such as band occupations, are automatically detected.
If not set, parameters such as the cutoff for the bare and screened Coulomb
potential are also read from the wave function and dielectric matrix,
respectively.

5) Automatic solution of Dyson's equation in FF calculations.
BerkeleyGW now automatically solves Dyson's equation for FF calculations. It uses
a varying number of frequencies to find the graphical solution for the
quasiparticle energies, and perform extrapolation (with appropriate warning
messages) if no intersection could be found. The code will also output the files
"eqp0.dat" and "eqp1.dat" directly, containing the off-shell and on-shell
quasiparticle energies.

6) Added ABINIT wrapper.
It is possible to interface the ABINIT code with BerkeleyGW. For now, the
wrapper can only output complex-valued wavefunctions, even for systems with
inversion symmetry.

Improvements

1) Added support for Xeon-Phi Knight's Landing (KNL)-based systems.

2) Improved OpenMP scaling throughout.
Using OpenMP is now recommended for large-scale computations.

3) Added new and more performant HDF5 file formats for epsmat and bsemat matrices.
This is recommend as default for all builds. Note that files are generally not
compatible with BerkeleyGW 1.1 and earlier. Binary epsmat files can be
converted to the HDF5 format with the epsmat_old2hdf5 utility. Older epsmat.h5
files from BerkeleyGW-1.1-beta2 can be converted to the current format with the
epsmat_hdf5_upgrade utility.

4) Added parallelization over frequencies in the epsilon code.
This allows for better scalability in full-frequency calculations. This
scheme is supported in the old Adler-Wiser and in the new Contour-Deformation
formalisms.

5) Improved the Monte-Carlo average scheme used to compute the Coulomb potential. [*]
For bulk systems, the new default scheme is to compute the average of Coulomb
potential v(q+G) for all q-points and G-vectors. We use a hybrid scheme to make
this evaluation faster. While the code is slightly slower for small calculations,
results should converge much faster with k-point sampling. One can still use the
old defaults with the input option "cell_average_cutoff 1.0d-12". Note that
no change was performed for 2D, 1D and 0D systems, or 3D metals.

6) Rewrote k-point interpolation engine. [*]
The previous k-point interpolation scheme used in the haydock, absorption, and
inteqp codes used a greedy algorithm to search for the closest coarse-grid points
around each fine-grid points, which lead to discontinuities of the interpolands.
The new interpolation engine uses QHull, which is bundled with BerkeleyGW, to
perform a Delaunay tessellation of the coarse-grid k-points. The new interpolation
scheme is much more robust. You can use the old interpolation scheme with the
"greedy_interpolation" flag.

7) Generalized scheme for k-point interpolation.
The k-point interpolation is used in the haydock, absorption, and inteqp codes.
The new scheme is useful for metals and systems with valence-conduction band
character mixing in the BSE.

Misc

1) Changed logic to deal with invalid GPP frequency modes. [*]
When the code performs a HL-GPP or a GN-GPP calculation and finds an invalid
mode with frequency with \omega_{G,G`}^2
within the static COHSEX approximation (i.e., move frequency to infinity).
The previous behavior was to "find" a purely complex mode frequency and relax
the causality constraint. One can switch which strategy to use with the
"invalid_gpp_mode" input flag.